At present, there are following well-known metal detection ways. One is item identification based on the X-ray penetration technology, that is, a diagnostic image is generated using radiography and other technologies to identify items such as metal. X-ray, as one of rays such as ionizing radiation dangerous to the human body, is mainly applied in the field of medical examination. At present, this detection way is employed in the available luggage security inspection instruments. Another way is detection of the presence of metal by detecting the impact of metal to the electromagnetic field by utilizing the principle of electromagnetic induction. At present, a global leading hand-held metal detector may detect the presence of gold of 0.13 g. The detection of the presence of ferrous metals is more difficult than that of nonferrous metals, because the induction of ferrous metals to a magnetic field is quite low.
For the first detection way, the implementation cost is quite high; it is difficult to transport and move the resulting products as they are huge and bulky; and the X-ray is seriously harmful to the human body. Whereas, the second detection way by utilizing the principle of electromagnetic induction requires short-distance detection, although it is lower in cost and less harmful to the human body than the first detection way. Hand-held instruments of this type requires detection close to the human body, while fixed door-shaped instruments of this type are not flexible for movement and the detection scope is narrow. Therefore, for both ways, the cooperation of a person to be detected is required, and the completion of corresponding actions or arrival at a specified position is required. The scope and speed of detection is greatly limited.